1. Field of the Invention
The present invention relates to a remote temperature-pressure recording system and, more particularly, a system for recording with respect to time, temperature or other analog voltage information (such as a signal from a pressure transducer), as received over a plurality of analog input channels, and for playing back the recorded information, one channel at a time, for display (typically, on an X-Y plotter).
2. Description of the Prior Art
In certain industrial applications--for example, in those applications involving the maintenance of carefully controlled (temperature-controlled, pressure-controlled, etc.) environmental conditions--it has been desirable to employ thermocouples and other measuring devices for the purpose of recording the environmental conditions within certain otherwise inaccessable places (such as, ovens, pasteurizers, etc.).
In such industrial applications, several problems have presented themselves. Firstly, it has been considered desirable to record, with respect to time, more than just one or two environmental parameters during the carrying out of the particular industrial process. Moreover, it has been considered desirable to record the plurality of environmental parameters, with respect to time, on a single device.
Furthermore, it has been recognized that certain environmental parameters, in the course of an industrial process, change more rapidly than others. Accordingly, insofar as measurement of these various environmental parameters is concerned, it has been considered desirable to equip such recording units with the capability of operator adjustment of sampling rate (that is, the frequency or lack of frequency with which the analog voltage information is to be sampled and recorded), and preadjustment to accomodate either extremely high or extremely low range parameter values.
Since, in many such industrial applications, it is necessary for the same parameter (such as, for example, temperature) to be measured at different stages along the path of a particular product or item as it moves through an industrial process, it is considered desirable to develop a recording unit which is not only small and insulated from the environmental conditions, but also battery operated, thus precluding the necessity of wires trailing as the device moves through the industrial process.
Inasmuch as various electric circuits, especially measuring circuits, are adversely influenced by "drift" or D.C. offset in the electrical system, it is also considered desirable to record, at prescribed intervals, a zero-voltage value, which value can be later examined to determine the effect of "drift" or D.C. offset on the measurements of the parameters over time.
Furthermore, whereas (on the one hand) it is considered desirable to have a single device comprising the recording and playback units of the recording system, it is (on the other hand) desirable to avoid subjecting both the recorder unit and the playback unit to the environmental conditions which must necessarily be experienced by the recorder unit as it moves through an industrial process recording data therein. Accordingly, it is considered desirable to have separate recorder and playback units which, however, may be joined--for example, by a plug connection--during the post-process period so as to facilitate playback of the recorded data, and display thereof.
Moreover, since--after each recording period during the industrial process--it will be necessary to recharge the battery of the battery-powered recorder unit, it would be desirable to accomplish this recharging of the recorder unit's batteries not only during a normal recharging period, set aside for that purpose, but also during the "playback" phase of operation, that is, during that time period when the recorder unit is "plugged into" the playback unit for the purpose of playback of data previously recorded.
Finally, it would be desirable to equip the playback unit with the capability of displaying, during playback, via a display unit separate from the data display, the particular channel for which the data is currently being played back.